A fuel cell includes an electrolyte layer and a pair of electrodes placed on either side of the electrolyte layer, and generates electricity through an electrochemical reaction between fuel gas such as hydrogen and alcohol and oxidizing gas such as oxygen and air, which are supplied to the corresponding electrodes, with the aid of a catalyst. Depending on the electrolytic material used for the electrolyte layer, the fuel cell may be referred to the phosphoric acid type, solid polymer type or molten carbonate type.
In particular, the solid polymer electrolyte type fuel cell (SPFC) using an ion-exchange resin membrane for the electrolyte layer is considered to be highly promising because of the possibility of compact design, low operating temperature (100° C. or lower) and high efficiency, as opposed to the solid oxide type fuel cell (SOFC).
The SPE typically includes an ion-exchange resin membrane made of perfluorocarbonsulfonic acid (Nafion: tradename), phenolsulfonic acid, polyethylenesulfonic acid, polytrifluorosulfonic acid, and so on. A porous carbon sheet impregnated with a catalyst such as platinum powder is placed on each side of the ion-exchange resin membrane to serve as a gas diffusion electrode layer. This assembly is known as a membrane-electrode assembly (MEA). A fuel cell can be formed by defining a fuel gas passage on one side of the MEA and an oxidizing gas passage on the other side of the MEA by using flow distribution plates (separators).
Typically, such fuel cells are stacked, and the flow distribution plates are shared by the adjacent fuel cells in the same stack.
When operating a fuel cell in a stable manner, it is essential to control the flow rates of the gases according to the temperatures of the gases and electrolyte, and the gas flow rates. For instance, Japanese patent laid open to publication No. 8-185878 and Japanese patent laid open to publication No. 11-162490 teach the provision of sensors in a fuel cell for detecting the temperatures and flow rates of the reaction gases.
However, according to such previous proposals, because the sensors are provided outside the fuel cell, it is not possible to obtain the desired information from each individual cell, and this prevents an accurate detection and control. Japanese patent laid open to publication No. 11-162490 discloses voltage sensors and resistive sensors which are installed in a fuel cell stack. However, installing the sensors m such a way creates the need for a highly complex sealing arrangement. This not only complicates the assembly work for the fuel cell stack, but also causes some difficulty in ensuring the durability of such a sealing arrangement. This problem is particularly serious when a sensor is desired to be installed in each fuel cell of a fuel cell stack.